1. Field of the Invention
The invention is directed to a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, wherein the clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission.
2. Description of the Related Art
A clutch device of this type is known, for example, from EP 0 931 951 A1. The clutch device serves to connect the drive of a motor vehicle with a multiple-speed shift transmission via two friction clutches which are preferably automatically actuated, wherein a disengagement or release system is allocated to each of these two friction clutches, so that the two friction clutches can be engaged or released independently from one another. A clutch disk of one of the two friction clutches is arranged on a central transmission input shaft so as to be fixed with respect to rotation relative to it, while a clutch disk of the other friction clutch engages at a second transmission input shaft so as to be fixed with respect to rotation relative to it, this second transmission input shaft, constructed as a hollow shaft, enclosing the central transmission input shaft. The known double-clutch is arranged with a fixed thrust plate of one friction clutch at a flywheel of an internal combustion engine. To this extent, the arrangement of the double-clutch in a drivetrain substantially corresponds to the arrangement of conventional (single)friction clutches in the drivetrain.
Double-clutch devices (called simply double-clutches) of the type mentioned above have attracted great interest recently and are generally formed of two wet or dry clutches which are switched alternately, possibly also with overlapping. Particularly in connection with a multiple-speed shift transmission, clutches of this type make it possible to carry out shifting processes between two respective transmission speeds of the transmission without interruption of tractive forces.
In principle, double-clutch devices make it possible for both clutches to be applied jointly in especially difficult starting situations, particularly those common in car racing. For this purpose, the accelerator pedal can be deflected to its stop, as the case may be, while the motor vehicle is kept essentially stationary at the same time by applying the maximum braking force until the clutch has reached its optimal transmission point. When the braking action is canceled at the moment of reaching the optimal transmission point, the vehicle is started with maximum acceleration. Starting processes of this kind are also considered for motor vehicles with a relatively weak engine under extreme starting conditions, for example, when starting on an obstruction; that is, they are not considered only for racing cars.
Obviously, starting processes of the type described above lead to high slippage with a correspondingly extensive development of heat. This presents the problem of carrying away this heat from the area of the friction clutch serving as starting clutch. Further, a correspondingly high wear of the friction clutches must be taken into account. Moreover, heating of the friction clutches is accompanied by changes in the coefficient of friction of the friction clutches, so that control of the release mechanisms of the two friction clutches, and therefore control of the two friction clutches relative to one another, can be appreciably impaired. Since inaccuracies or changes in the functional matching of the two friction clutches relative to one another caused by heat can have the result that a torque ratio not intended in the shifting process is applied to the transmission input shafts, shifting processes in the shift transmission can be subjected to load. The synchronization in the shift transmission can be overtaxed in this way, so that, in the worst case, the shift transmission can be damaged to the point of complete failure, apart from disadvantages with respect to efficiency which occur in any case. On the whole, mismatching between the two friction clutches caused by heat is incompatible with a problem-free torque transmission in shifting processes in the shift transmission without interruption of tractive force and without jerking during shifting.
Another problem area in a double-clutch device relates to starting processes carried out in opposition to an inclination, wherein the motor vehicle must be prevented from rolling backward, or those which are used when parking at the lowest possible speed, for example, for precise positioning of a motor vehicle in a parking space. The operating states mentioned above are referred to in technical circles as xe2x80x9chill-holdingxe2x80x9d and xe2x80x9ccreepingxe2x80x9d. Both starting processes have in common that the friction clutch serving as starting clutch is operated, sometimes without actuation of the accelerator, over a longer period of time with slip. Although the torques to be transmitted in such starting processes lie well below those occurring under the operating conditions described above, especially in car racing, an intensive heating of the respective friction clutch or even both friction clutches can occur, resulting in the problems detailed above.
Suggestions have been made for gear-shifting strategies and shifting processes for double-clutch transmissions based on the aimed for adjustment of clutch slip (DE 196 31 983 C1) with consequent generation of friction heat. Depending on driving behavior, overheating problems of the type mentioned above cannot be ruled out.
The risk of intensive overheating exists not only in a dry friction clutch, but can also occur in so-called xe2x80x9cwetxe2x80x9d friction clutches, in the form of a disk or plate clutch, which are operated by the action of a viscous operating medium such as hydraulic fluid. By way of example, a gear change box with two plate clutches is known from DE 198 00 490 A1, wherein one plate clutch is provided for forward driving and the other for driving in reverse. DE 198 00 490 A1 is concerned primarily with providing adequate cooling of the two plate clutches using the viscous operating medium. In spite of the liquid cooling, heating of the friction clutches is also a considerable problem in plate clutches because the operating medium, which usually flows through friction facing grooves or the like to carry off the heat, cannot be guided between the plates in optional quantity. The reason for this is that, on one hand, excessive flow through the friction facing grooves or the like would build up a counterpressure between the friction surfaces of two adjacent plates and would therefore reduce the capacity of the friction clutches to transmit torque (with a corresponding increase in slip and therefore additional generation of friction heat, so that the problem of overheating is exacerbated) and, on the other hand, the operating medium could be overheated and destroyed when flowing through between the plates. Overheating in plate clutches can result in that the friction surfaces can no longer separate from one another completely during a disengaging process and, consequently, torques can still be transmitted via the clutch which should be disengaged, so that considerable drag torques can reach the associated shift transmission. When plates clutches are used in a multiple-clutch device, especially a double-clutch device, of the type mentioned above, shifting processes could again be brought under load in the shift transmission with resulting overtaxing of the synchronization in the shift transmission.
One approach to mastering overheating problems in the area of friction clutches in case of unfavorable operating conditions, for example, with problematic starting processes in a motor vehicle, is to provide another starting element in addition to the first and second clutch arrangements which is in the form of a hydraulic clutch or hydrodynamic clutch and comprises a hydrodynamic circuit with an impeller wheel, a turbine wheel and, if desired, a stator wheel. The driving member can be connected in parallel with one of the two friction clutches; that is, it can act on a common transmission input shaft irrespective of the engagement state of this friction clutch. A clutch device in which two plate clutches and a starting element of this type are integrated, was described in the German Patent Application 199 46 857.5 by the present Applicant which was applied for on Sep. 30, 1999 and whose disclosure is incorporated in the subject matter disclosed in the present application.
Within the framework of investigations undertaken by the present Applicants in connection with double-clutch devices, it was shown in general that wet-type clutches exhibit sealing problems and problems relating to output losses. Further, it was shown that boundary conditions relating to the available axial and radial installation space could be adhered to only with difficulty, if at all, based on the previously known concepts. With regard to clutches, possibly, diaphragm clutches, which are actuated by pistons integrated in the clutch device, the arrangement of the piston chambers associated with the pistons proved especially problematic.
The object of the invention is generally to achieve improvements with respect to at least one of the problems and/or other problems mentioned above. In particular, an objective of the invention is to achieve improvements with respect to the bearing support and arrangement of the multiple-clutch device in the drivetrain.
According to one aspect of the invention, the invention provides a multiple-clutch device, i.e., a double-clutch device, for arranging in a drivetrain of a motor vehicle between a drive unit and a transmission, wherein the clutch device has a first clutch arrangement associated with a first transmission input shaft of the transmission and a second clutch arrangement associated with a second transmission input shaft of the transmission for transmitting torque between the drive unit and the transmission, wherein at least one of the transmission input shafts is constructed as a hollow shaft and one of the transmission input shafts extends through the other transmission input shaft constructed as a hollow shaft.
It is provided according to the invention that a bearing arrangement is associated with at least one of the clutch arrangements, wherein the latter is supported or can be supported by means of the bearing arrangement on at least one of the transmission input shafts, preferably at least at the radial outer transmission input shaft which is formed as a hollow shaft, so as to be rotatable relative to it.
The bearing support of the clutch system provided, according to the invention, at the transmission shafts is particularly advantageous in that the dependency of the system on tolerances is reduced. A bearing support at the transmission housing is preferably done away with, or only a support which is not problematic with respect to tolerances is provided at the transmission. The bearing arrangement is preferably constructed as an axial and radial bearing arrangement for axial and radial support of the clutch arrangement at the at least one transmission input shaft. However, providing a bearing arrangement constructed only as an axial bearing arrangement or only as a radial bearing arrangement is also advantageous for many installation situations. In the case of diaphragm clutches, it is generally advantageous to use bearings offering both axial and radial support for the bearing support of the plate carriers.
An advantageous embodiment form is characterized in that the clutch arrangements have a common, possibly tubular, ring part by which they are mounted or can be mounted at least at one transmission input shaft. The common ring part is mounted or can be mounted on the at least one transmission input shaft via the bearing arrangement mentioned above.
An input side of the respective clutch arrangements can be connected with the ring part so as to be fixed with respect to rotation relative to it, preferably in such a way that the torque flow from the drive unit to the input side of one of the clutch arrangements runs via the input side of another of the clutch arrangements and via the ring part.
At least one of the clutch arrangements can have an actuating piston defining the pressure chamber for actuation, preferably for engagement of the clutch arrangement by means of a pressure medium, preferably a hydraulic medium. In this respect, it is advantageous when the actuating piston is guided so as to be axially displaceable at the ring part and so as to seal the pressure chamber. This step contributes to a compact construction of the clutch device.
The ring part can have at least one pressure medium channel for supplying the pressure chamber with pressure medium. In this case, it is preferable that a transmission-side connection sleeve which is possibly fixed with respect to the transmission is associated with the ring part so that the ring part is received in the connection sleeve so as to be rotatable relative to it and so as to seal at least one pressure medium connection of the pressure medium channel and so as to adjoin the pressure medium source. In this way, the pressure chamber can be connected to an associated pressure medium supply without great assembly effort when assembling the drivetrain.
In order to provide compensation for centrifugal force, the actuating piston can divide the pressure chamber from an associated centrifugal force pressure compensation chamber holding a pressure compensation medium. For this purpose, it is suggested that the centrifugal force pressure compensation chamber is connected to a pressure compensation medium supply which, if desired, is formed by a hydraulic medium supply or a separate operating fluid supply, possibly an operating oil supply.
According to an advantageous construction, a fluid supply channel runs between the ring part and the at least one transmission input shaft for supplying at least one of the clutch arrangements and/or at least one other functional unit of the clutch device with operating fluid, preferably operating oil. It is primarily intended that the operating fluid serves as a cooling fluid which cools the clutch arrangement.
The fluid supply channel running between the ring part and the at least one transmission input shaft can also be used for supplying the centrifugal force pressure compensation chamber, if any, with pressure compensation medium. For this purpose, it is suggested that the ring part has substantially radially extending operating fluid passages for connecting the centrifugal force pressure compensation chamber to the operating fluid supply via the fluid supply channel.
With regard to the fluid supply channel, it is suggested generally that the fluid supply channel is guided through the bearing arrangement; that is, the latter allows operating fluid to pass through it.
Above all, it is intended that at least one of the clutch arrangements, preferably both the first and second clutch arrangement, is/are constructed as a plate clutch arrangement. However, other clutch arrangements can also be considered.
Further independent aspects of the invention will be discerned by the person skilled in the art from the following explanations and the description of the drawings.
The invention is further directed to a drivetrain for a motor vehicle with a clutch device, according to at least one aspect of the invention, arranged between a drive unit and a transmission.
The invention will be described more fully in the following with reference to embodiment examples shown in the Figures.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.